The invention relates to a needle set, in particular for knitting machines.
Knitting machine needles have an elongated shank, usually formed from a flat material, from which one or several butts extend laterally away. The butts are used for displacing the needles linearly in a needle groove. To this end, they are connected with a so-called cam. The butts travel through a cam groove by means of a relative movement of the cam in respect to the needles, or the needle bed receiving them, and in this way cause the linear displacement of the needle. As a rule, this functions absolutely dependably. However, at times collisions between the needle butts and parts of the cam can occur because of erroneous control of components of the needle cam, as well as other accidental occurrences. These must not be allowed to result in damage to machine parts of the knitting machine, in particular damage to the cam or the needle bed. The needle bed is constituted by a multipart solid body, into which closely arranged grooves in accordance with the mostly relatively narrow distribution have been cut, which constitute needle grooves. Partitions are provided between the individual grooves, which laterally guide the needles. It is necessary, even in case of a malfunction, to prevent damage to such partitions or other damage to the needle bed.
A needle for knitting machines is known from JP 620191888, whose butt has predetermined breaking points. These are constituted by notches formed on the long narrow sides of the butt, which cause a specific weakening of the butt. The latter can break off in case of a collision of the butt with cam elements, so that damage to the needle bed can be prevented to a large extent.
Moreover, knitting machines exist which require needles of different butt lengths. For example, such needles are required if needles of the same needle bed are to be moved over different lengths in the course of the knitting process. In this case it is intended that long butts come into engagement with other cam elements than short butts.
Based on the foregoing, it is the object of the invention to design the needles in such a way that the damage of machine elements of the knitting machine because of collisions between cam or selecting elements with needle butts are prevented even if the needle butts are of different lengths.
This object is attained by means of the needle set in accordance with claim 1.
The needle set, or the needle family, in accordance with the invention has at least two, but preferably three or more needles, whose loop-forming elements are identical, wherein the butts of these needles are of different lengths. The butts are provided with predetermined breaking points which establish different breaking resistances. If the breaking resistance is great, a relatively large breaking torque is created during the breaking process, which attempts to turn the needle around its longitudinal axis. This breaking torque must be absorbed by the needle bed. The different needles of the needle family, or of the needle set, now have different breaking torques. These are preferably matched in such a way that the largest occurring breaking torques cannot damage the needle groove, or the needle bed. On the other hand, the breaking torques are preferably set in such a way, in particular in view of the length of the butts, that forces of approximately the same size are required for developing the different breaking torques at each of the butt ends or butt tips. This measure in turn prevents damage to cam elements. Finally, the predetermined breaking points are dimensioned in respect to the breaking torque, which occurs because of a strain on the butts in the axial direction of the needle, i.e. when the driving force is transmitted, in such a way that all needles of the needle set can permanently tolerate even the largest occurring driving force.
The predetermined breaking points are embodied in such a way that a larger breaking torque is required for needles with longer butts than for needles with shorter butts. This can be achieved in that the predetermined breaking points between the needle types differ in regard to their size and/or their shape and/or their position. Larger breaking torques of the longer butts primarily relate to a strain on the butt which extends approximately vertically on its flat side. Regarding the driving torque, the breaking resistance of the butts is preferably substantially the same. This can be achieved in that the predetermined breaking points are constituted by depressions which are formed on the flat side of each butt approximately parallel in respect to the longitudinal direction of the needle. These depressions hardly weaken the butt in respect to the transmission of the driving force (along the needle). But they permit an easier breaking in case of a strain on the butt transversely in respect to the needle. By means of this a particularly good protection of the machine bed and of the cam is achieved, without limiting the operating ability and service life of the needle.
Depressions, which are formed parallel in respect to each other and to the longitudinal direction of the needle, and are located outside of the needle bed, are preferably embodied on both flat sides as predetermined breaking points. They are therefore approximately arranged in the area of the transition from the needle shank to the butt, or even slightly distant from the needle shank. They are preferably located on a common plane extending vertically in respect to the flat side of the butt. In addition it is advantageous if the predetermined breaking point is arranged in an area located between the cam and the needle bed. In this way it is possible to achieve that no damage to the machine occurs as a result of a needle break.
The predetermined breaking points are constituted by grooves, for example, which are rounded. Preferably the radii of all predetermined breaking points of the needles of a needle family are identical wherein, however, the depths of the respective depressions are different. The breaking resistance can be regulated by means of the amount of depth. In this case the length of the depression essentially corresponds to the width of the butt, i.e. preferably the depression extends over the entire flat side of the butt.
It has been shown that a needle bed can easily absorb the relatively large breaking torques which the needle set of the invention assigns to the needles with long butts, so that even long butts are maintained dependably and solidly on the needle shank. On the other hand, it has been shown that the low breaking torques of short-butted needles are completely sufficient for transmitting the desired driving forces and for achieving the required service life.